1. Technical Field
The present invention relates to a new fullerene derivative useful as an organic semiconductive material and a method of preparing the same.
2. Description of the Related Art
Organic semiconductive materials are well studied in an organic electronics field such as organic transistors and organic ELs. Further, an organic solar battery using a fullerene derivative as an organic photoelectric conversion element is strenuously studied. As the most famous fullerene derivative in this field, [6,6]-phenylC61-butyric methyl ester (PCBM) which is soluble in an organic solvent is disclosed in J. Org. Chem. 1995, 60, 532-538. A functional group having a suitable size is introduced to the fullerene and solubility in an organic solvent is adjusted to increase an area of a pn bonded interface which is a charge generation area and photoelectric conversion efficiency. However, the photoelectric conversion efficiency is still insufficient, and a better fullerene derivative is required.
Japanese published unexamined applications Nos. JP-2011-26235-A, JP-2011-35116-A, JP-2011-77486-A, JP-2011-93848-A, JP-2011-98906-A and JP-2011-121886-A disclose fullerene derivatives various functional groups are introduced to for the purpose of improving an open end voltage and expanding absorption wavelength area. Bulky functional groups are introduced to the fullerenes to improve solubility in an organic solvent, and further, compatibility with a p-type semiconductive material is increased to improve photoelectric conversion efficiency. However, being short of solubility in an organic solvent, these are unable to construct a close bulk hetero junction structure in combination with the low-molecular-weight p-type semiconductive material expected to have particularly high durability, and do not have sufficiently satisfactory photoelectric conversion efficiency.